I don’t dispute your claim. I agree with it.
If you look at the pool landing page, the number of active NTP servers in Africa is 102 and in South America it is 76. I think that is too few for both, keeping in mind the internet populations. The question then is, from where do you add servers? Just randomly, or just looking at geographical distance, or something else, or a mix?
If you just look at the geographical distance, Africa and South America are fairly close and there are even undersea cables between them. But there are already too few NTP servers in both, so that won’t help. From the southern parts of Africa, Australia looks fairly close, but at least from my internet connection, packets either take the long way around, via SACS, MONET, Miami…, at around 430ms, or via Amsterdam, Singapore,…, at around 480ms, depending on which Australian ISP is being used. In both these cases, it would go through an region with an “abundance” of ntp servers in the pool.
But Africa is well connected to Europe, which is also the continent with the most active NTP servers in the pool. Actually for NTP pool purposes, grouping the African countries that border the Mediterranean Sea with Europe, would probably be a win for them.
I guess ideally every NTP client would have a mini NTP monitor that would figure out the ideal servers to use, also keeping diversity and the server load in mind. 